The team behind Preakness Stakes favourite Nyquist is not concerned about rain which could advantage his main rival Exaggerator.

The National Weather Service has forecast an almost 100 per cent chance of rain beginning early Saturday (Sunday AEST) and continuing throughout the day.

Nyquist is the 3-5 favourite to add the second leg of the Triple Crown to his Kentucky Derby win.

"With a horse like Nyquist, I'm not overly concerned about the weather," trainer Doug O'Neill said.

"As far as rain or shine, we're not going to change anything shoeing-wise He's going to wear the same shoes he's got on."

Rain could be a good thing for several of his rivals, especially Derby runner-up Exaggerator who won the Santa Anita Derby on a sloppy track.

Nyquist, with an 8-0 record, won the Florida Derby over a surface listed as good even though the track had been drenched by a rainstorm before the race.

He has 10 rivals over the 1-3/16 miles (1900m) at Pimlico and jumps from gate three with Mario Gutierrez aboard.

O'Neill has been through this before, along with owner J Paul Reddam and Gutierrez. In 2012, they won the Derby and Preakness with I'll Have Another who was retired the day before the Belmont with an injury.

"He has so much speed away from the gate," O'Neill said.

"Ideally, he gets good position wherever that is and he runs a big race."

Exaggerator, the 3-1 second choice, may be the most accomplished mud runner in the field. In addition to his Santa Anita Derby win, he has won once and finished second on wet tracks.

"He's run on every track that's been put before him and that may prove to be an advantage," Exaggerator's trainer Keith Desormeaux said.

Lani, the first Japanese-trained horse in the Preakness, is the only other Derby starter in the field.

He has run three times on "off-tracks" in Japan, with a win, a second and a fifth.

"It would not be great, but everybody has to run on it," Lani's trainer Mikio Matsunaga said of a possible wet track.